Lubricating oil compositions

Abstract

A lubricating oil composition, a method of reducing low-speed pre-ignition (LSPI) in a direct-injected spark-ignited internal combustion engine, and a use of a lubricant composition to reduce LSPI events in such an engine. Preferably, the composition comprises a detergent package comprising a borated calcium detergent, wherein the detergent package provides a calcium content in the composition of at least 0.12 mass %, based on the total mass of the composition, and wherein the borated calcium detergent provides a boron content in the composition of at least 100 ppmm, based on the total mass of the composition. Optionally, the composition comprises a first detergent comprising a calcium detergent, and a second detergent comprising a borated calcium detergent.

What is claimed is: 
     
       1. A method of reducing low-speed pre-ignition (LSPI) events in a direct-injection spark-ignition internal combustion engine comprising:
 lubricating the crankcase of the direct-injection spark-ignition internal combustion engine with a lubricating oil composition prior to operating the engine, in which operation the engine generates a break mean effective pressure level of greater than 1,500 kPa, at engine speeds of from 1,000 to 2,500 rotations per minute (rpm), thereby reducing LSPI events during such operation, the composition comprising a detergent package comprising a borated calcium detergent; 
 wherein, the detergent package provides a calcium content, as measured by ASTM 4951, in the lubricating oil composition of at least 0.12 mass %, based on the total mass of the lubricating oil composition, and wherein the borated calcium detergent provides a boron content, as measured by ASTM D5185, in the lubricating oil composition of at least 100 ppmm, based on the total mass of the lubricating oil composition, and 
 wherein the boron content from the borated calcium detergent is more efficient at reducing frequency of LSPI events during operation of the engine than an equivalent boron content introduced into the composition by means of a borated dispersant. 
 
     
     
       2. A method according to  claim 1 , wherein the borated calcium detergent comprises a borated overbased calcium detergent and has a TBN of at least 150 mg KOH/g, as measured by ASTM D2896. 
     
     
       3. A method according to  claim 1 , wherein the detergent package additionally comprises a further detergent. 
     
     
       4. A method according to  claim 1 , wherein the detergent package provides a calcium content, as measured by ASTM 4951, in the lubricating oil composition of at least 0.14 mass %, based on the total mass of the lubricating oil composition. 
     
     
       5. A method according to  claim 1 , wherein the detergent package provides a calcium content, as measured by ASTM 4951, in the lubricating oil composition of at least 0.16 mass %, based on the total mass of the lubricating oil composition. 
     
     
       6. A method according to  claim 1 , wherein the detergent package provides a calcium content, as measured by ASTM 4951, in the lubricating oil composition of at least 0.18 mass %, based on the total mass of the lubricating oil composition. 
     
     
       7. A method according to  claim 1 , wherein the borated calcium detergent provides a boron content, as measured by ASTM D5185, in the lubricating oil composition of at least 150 ppmm, based on the total mass of the lubricating oil composition. 
     
     
       8. A method according to  claim 1 , wherein at least 50%, of the boron content of the lubricating oil composition is provided by the borated calcium detergent. 
     
     
       9. A method according to  claim 8 , wherein 100%, of the boron content of the lubricating oil composition is provided by the borated calcium detergent. 
     
     
       10. A method according to  claim 3 , wherein the further detergent comprises non-borated calcium detergent. 
     
     
       11. A method according to  claim 10 , wherein:
 the non-borated calcium detergent comprises a calcium phenate, a calcium sulfonate and/or a calcium salicylate; and 
 the borated calcium detergent comprises a borated calcium phenate, a borated calcium sulfonate and/or a borated calcium salicylate. 
 
     
     
       12. A method according to  claim 10 , wherein the borated calcium detergent comprises a borated analogue of the non-borated calcium detergent. 
     
     
       13. A method according to  claim 10 , wherein the borated calcium detergent comprises calcium and boron in a calcium mass % to boron mass % ratio of 1:Z, based on the mass of the borated calcium detergent, wherein Z is at least 0.1. 
     
     
       14. A method according to  claim 13 , wherein Z is from 0.1 to 4. 
     
     
       15. A method according to  claim 10 , wherein the non-borated calcium detergent and the borated calcium detergent are present in a ratio of non-borated detergent mass % to borated detergent mass % of 1:X. based on the total mass of the lubricating oil composition, wherein X is at least 0.1. 
     
     
       16. A method according to  claim 15 , wherein X is from 0.1 to 10. 
     
     
       17. A method according to  claim 10 , wherein the non-borated calcium detergent has a calcium content of from 2 mass % to 16 mass %, based on the mass of the non-borated calcium detergent, and/or the borated calcium detergent has a calcium content of from 4 mass % to 16 mass %, based on the mass of the borated calcium detergent. 
     
     
       18. A method according to  claim 10 , wherein the second detergent has a boron content of from 1 mass % to 10 mass %, based on the mass of the second detergent.